Method of shaping vitreous tubes



A. GREINER 2,561,859

METHOD OF SHAPING VITREOUS TUBES Filed NOV. 5, 1949 Fig 5. a

Patented July 24, 1951 UNITED STATES PATENTOFFIGEJ METHODOF SHAPING vrrasoos TUBES Alfred Greiner, Cleveland Heights, .0hio;;assignor to General Electric Company, a corporation of.

New York Application November 3, 1949, Serial No:125,315

6 Claims.

This invention relates. to methods of making.

vitreous tubes having straight parallel portions and? particularly to methods of making. U-shaped glass tubes useful. as. envelopes for discharge devices, such as fluorescent and'germicidal discharge lamps.

Glass tubes having a u shape have heretofore been formed by bending a straight tube either byhand or mechanically. In order to get a satisfactory U-bend, so that the legs will be parallel and of thesame length; the tube mustrbe/ heated exactly in the middle and quickly bent to the desired shape. This inherently results in a thin wall on theoutside of the bend. If a heavier-walled tubing is used in order to make a practical outer wall thickness at the bend, the inner wall tends to'corrugate or buckle; This effeet; is: particularly troublesome when a sharp bend is made; i. a, when very little spacing: is desiredbetween the legs of the finished'tube. The bending operation also becomes much more'diifi cult as the diameter of the tubing is increased. to the size usual for fluorescent or "germicidal lamp envelopes.

An object of my invention is to provide a method of making a vitreous tube having parallel, closely-spaced straight portions united by a curved portion and having a substantially uniform wall thickness throughout.

Another object is to provide a method of forming a U-shapedtube having closely spaced legs.

A further objectof my invention is to provide amethod whose effectiveness in forming U-shaped tubes is independent of the tube diameter and.

which is particularly useful in easily forming U'-tubes of a large diameter.

A featureof my invention which attains the drawing; Fig; 2 is a similar View of the lower end of the tubes showing apair of gas burners for heating themand a glass working tool; Fig.

3 is a bottom plan view after the tubes shown in.

2 have-been joinedby the too1;rFig,. 4 israzr softeningtemperature by the usual gasfiame usedsimilar view of the 'joined tubes after continued: heatingof theirrjuncture; .Fig. 5 is-a perspective: viewer the lower tube-1 ends joined togetherxandi" a pair-of. gas burnersfor heating the joinedends; Fig. 6 is a similar view of thetube ends. closed and a fragmentaryview of a glass working: '7 is a'frontelevational: view on a reduced scale of 'a .U -shaped envelope made upof thetwo tubes, mounted in'axmoldrand. connected:

tool and. Fig.

to a source of air under pressure.

Referring toFigulfof the drawing; thexmetho'dr of making a U-shaped.tube'inraccordancewith;

myinven tion comprises. the. steps. of fgrippingtwo glass tubes 1 and 2: adjacentbne. of theirends. in a chuckhaving jaws3 'andt which holds'the. tubes I and tin closely spaced; side-by-sideparaI-I lel positionswith their lower ends terminating in. A- .pair of opposed gas ribbon" burnersii-andrfi each: having aseries of aligned openings orjets are directed between. the lower. juxtaposed ends of'the tubes l'and 2 to heatthe same plane.

their inside facingisurfaces to' the softeningtemperature of the .i-glass;

T is inserted inthe lower-endof each of the glass tubes! and 2, as'shown. in .Fig. 2,.andsthe-sofetened wall portions ofthe-tubesl and. 2 are first. cut by closing: the The walls of the lower.- open ends of the tubes! -and-2 4816: thus unitedu as shown at 8 in 3 into a composite Wall common to both tubes 1 and 2. On continued heating,

pressed together and then blades of the shearsl.

by-the burners ii and 6, the composite wall approaches an oval shape-incross-section as shown. in Fig.4 and definesan outwardly-openingcavity;

communicating with the: boresv of the tubesl and '2.

The outer opening of the cavity, is. thenclosed';

as shown inwFigs. 5'and16 .by directingthe opposed. ribbon burners. along thedotted line 9 transverse to the longitudinal axes of the tubesl and'z to heat the glass inr-a narrow zone including line 9 to its.softeningtemperature. The SOfltened glass :is then severed-by the shears I along; thedotted line 9 to close the opening as shown in Fig. 6. The culleti l0 dropsoil after severing...

Obviously, the. cullet .I 0 maybe melted ofi'bythe burners in' the usual manner and the use of thee shears 7 eliminated. The melting cit-of thecullet lircloses the opening as the cullet drops ofi. pulling. the softened glass walls together.

The preferred. final step in making the U-shaped tube consists in shapingthe bend by.

heating the glass which is to form the bend to its With the heatedxglass in. a plastic condition, one blade'of apair of shearsthe usual manner and sealing the tube.

The new method may be used successfully for making composite U-shaped tubes from two pieces of straight glass tubing of various diameters. For example, in making flourescent discharge lamps and germicidal lamps, it is com- 7 mon to use a straight tube approximately 1 /2 inches in diameter as the lamp envelope. A U-shaped tube having this diameter and a separation of only approximately e inch to /4 inch between the legs is readily fabricated by the method described'above without the disadvantages of variations in wall thickness or corrugated wall portions at the bendof the U -shaped tube characteristic of the prior attempts to bend a straight tube havinga diameter of this order intoya 'U-shapewith a separation between the legs .less than the diameter of the tube. When using 1%; inch diameter tubes to form a U-tube with'a separation is to /4-inch between its legs in accordance with the method of my invention, gas burners 3 inches long and inch wide are preferred in unitingthe open ends of the tube as'described in connection with Figs. 2 to 4.

The tubes are cut longitudinally by the shears for a distance approximately 3 inches from their open ends. In theoperation described in connection-with Figs. 5 and 6 the tubes i and 2 are cutv by the shears along the transverse line 9 approximately 1 inches from their open ends to close the bottom of the composite tube. -Of course, with tubes of other diameters, theabove distance of the-cuts may be suitably changed.

Obviously, the method-described above may be used to make up a composite tube having any desirednumber of closely spaced parallel straight portions by joining the ends of the composite tube to the ends of pieces of straight tubing or to other. similarly made the-same manner .that tubes l and 2 are joined together and the shape of mold ll maybe modified to shape the bends of such composite tube having a multiplicity. of closely spaced parallel straight portions. Such tube: is also useful as a discharge lamp envelope.

What I claim as new and desire to secure by Letters Patent of the United. States is:

1. method of joining vitreous tubes to form a composite tube having closely spaced portions connected by a 180 curved portion which comprises mounting open vend portions of a pair of vitreous tubes side-by-side and opening in the same-direction, heating to a plastic condition and then pressing together and cuttingthrough the facing wall portions of the tubes for a substantial distance inwardly from'their open ends to form a compositewall common to and uniting' said tubes, shaping the composite wall into an oval in cross section and to define an outwardly opening cavity communicating .with the bores of the tubes and then closing the outer opening of the cavity.

2. The method of joining vitreous tubes to form a composite tube having closely spaced composite tubes in portions connected by a curved portion which comprises mountingopen end portions of a pair of vitreous tubes side-by-side and opening in the same direction, heating to a plastic condition and then pressing together and cutting through the facing wall portions of the tubes for a substantial distance inwardly from their open ends to form a composite wall common to and uniting said tubes, shaping the composite wall into an oval in cross section and to define an outwardly opening cavity communicating with the bores of the tubes, heating to a plastic condition the composite wall adjacent the outer opening of the cavity and pressing the plastic walls together to close the said opening.

3. The method of joining vitreous tubes to form a composite tube having closely spaced portions connected by a 180 curved portion which comprises mounting open end portions of a pair of vitreous tubes side-byside and opening in the same direction, heating to a plastic condition the facing wall portions of the tubes for a substantial distance inwardly from the said open ends, progressively pinching together and immediately cutting through the plastic wall portions inwardly from the tube ends to unite the severed walls of the tubes into a composite wall common to both tubes, shaping the composite wall into an oval in cross-section and to define an outwardly opening cavity communicating with the bores of the tubes, and then closing the outer opening of the cavity.

41. The method of joining vitreous tubes to: form a composite tube having closely spaced curved portion portions connected by a 180 which comprises mounting open end portions of a pair of vitreous tubes side-by-side and opening in the same direction, heating to a plastic condition the facing wall portions of the tubes for a substantial distance inwardly from the said open ends, progressively pinching together and immediately cutting through the plastic wall portions inwardly from the tube ends to unite the severed walls of the tubes into a composite wall common to both tubes, shaping the composite wall into an oval in cross-section and to define an outwardly opening cavity communicating,

withv the bores of the tubes, heating to a plastic condition the composite wall adjacent the outer opening of the cavity, pressing the plastic sides of the oval-shaped wall together to close the outer opening and then molding the composite wall portion of the tube into a smooth rounded contour.

5. The method of forming a U-shaped vitreous tube having closely spaced legs which comprises vertically mounting two pieces of straight vitreous tubing in side-by-side parallel relation and spaced apart by the distance desired between the legs of the finished U-shaped tube, heating the inside facing surfaces of said tubes at the lower ends thereof'to a plastic condition, pressing to gether and cutting through the said plasticinside facing surfaces at the equivalent of the point of tangency for a distance upward from the bottom of the tubes of approximately twice the tube diameter thereby uniting the walls of,

said tubes for said distance, further heating the] composite wall so formed to increase the size of the transverse opening between said tubes defined by said wall, heating said wall to a plastic condition and pressing together and cutting through its plastic sides transversely to the axes of the united tubes and at the distance from the bottom equal to a tubediameter to close the bottom of the composite tube, and thereafter shaping the composite wall into a smooth rounded curve joining the legs of the U-shaped tube.

6. The method of forming a U-shaped vitreous tube having closely spaced legs which comprises vertically mounting two pieces of straight vitre- 011s tubing in side-by-side parallel relation and spaced apart by the distance desired between the legs of the finished U-shaped tube, heating the inside facing surfaces of said tubes at the lower ends thereof to a plastic condition, pressing together and cutting through the said plastic inside facing surfaces at the equivalent of the point of tangency for a distance upward from the bottom of the tubes of approximately twice the tube diameter thereby uniting the walls of said tubes for said distance, further heating the composite wall so formed to increase the size of the transverse opening between said tubes defined by said wall, heating said wall to a plastic condition in a narrow zone transverse to the axes of the united tube and at a distance from the bottom equal to a tube diameter or melt off the cullet and to close the bottom of the composite tube, and thereafter shaping the composite wall into a smooth rounded curve joining the legs of the U-shaped tube.

ALFRED GREINER.

No references cited.

Certificate of Correction Patent No. 2,561,859

July 24, 1951 ALFRED GREINER It is hereby certified that error appears in the printed specification of the above numbered iring correction as follows:

for or melt read to melt; and that the said Letters Pate nt should be read as corrected above rm to the record of the c es.

's 15th day of Ja 

